Acute effects of non‐weathered and weathered crude oil and dispersant associated with the deepwater horizon incident on the development of marine bivalve and echinoderm larvae

Acute toxicity tests (48 to 96 hours duration) were conducted with larvae of two echinoderm species (Strongylocentrotus purpuratus and Dendraster excentricus) and four bivalve mollusk species (Crassostrea virginica, Crassostrea gigas, Mytilus galloprovincialis, and Mercenaria mercenaria). Developing larvae were exposed to water‐accommodated fractions (WAFs) and chemically enhanced water accommodated fractions (CEWAFs) of fresh and weathered oils collected from the Gulf of Mexico during the Deepwater Horizon (DWH) incident. WAFs (oils alone), CEWAFs (oils plus Corexit 9500A dispersant), as well as WAFs of Corexit alone were prepared using low‐energy mixing. WAFs of weathered oils had no effect on survival and development of echinoderm and bivalve larvae, while WAFs of fresh oils showed adverse effects on larval development. Similar toxicities were observed for weathered oil CEWAFs and WAFs prepared with Corexit alone for oyster (C. gigas and C. virginica) larvae, which were the most sensitive of the tested invertebrate species to Corexit. Mean EC10 values for total polycyclic aromatic hydrocarbons and dipropylene glycol n‐butyl ether (a marker for Corexit) in this study were higher than all concentrations reported in nearshore field samples collected during and after the DWH incident. Our results suggest that water‐soluble fractions of weathered oils and Corexit dispersant associated with the DWH incident had limited, if any, acute impacts on nearshore larvae of eastern oysters and clams, as well as other organisms with similar sensitivities to those of test species in this study; however, exposure to sediments and long‐term effects were not evaluated. This article is protected by copyright. All rights reserved

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